1. Field of the Invention
Embodiments of the present invention relates to designs, fabrications, characterizations, and uses of new types of electrodeposited polymer coatings that offer both unique reversible wettability and electro-optical properties.
More specifically, embodiments of the invention enable the formation of superhydrophobic and superlipophilic conducting surfaces made from non-fluorinated conducting polymers. Such surfaces are built following a two-step approach, which is capable of being applied to a variety of materials. The precursor reagents or agents include non-fluorinated conducting polymers of pre-grafted hydrophobic chains that are first electrodeposited by anodic electropolymerization or chemical oxidative methods onto layers of polymer particles such as polystyrene particles pre-assembled on an electrode surface such as a gold (Au) surface. The layering of the particles such as latex microspheres provides the submicron size roughness of a biomimetic surface imitating a geometrical microstructure of a surface of a lotus leaf for example. The overall coatings described herein exhibit both tunable electrochromic and wettability properties that are tuned by applying an electric potential across the surface. Electro-optical properties may be controlled based on a level of doping and type of chemical structures utilized. Moreover, the use of surfactants on top of such coatings allows one to further tune the wettability behavior. While this work emphasizes the use of conducting polymers by anodic polymerization, the design may be extended to non-conducting polymers such as acrylate, styrene, vinyl functional groups using cathodic electropolymerization or chemical reductive methods instead of anodic electropolymerization. Also, the coating can be done on a variety of metallic, metal alloy, metal-oxide and non-metallic substrates of various size, shape, and geometry, provided the requirements for deposition of particles and polymers can be accomplished. Important applications of such coatings may be in the form of anti-wetting, filtration, anti-corrosion, de-icing, anti-microbial, electrochromic, and electrophoretic or electro-wetting applications, where the wetting properties of the film play an important role.
2. Description of the Related Art
The water-repellent behavior of a lotus leaf is a wonder of nature that marvels many scientists of diverse backgrounds. A lotus leaf will give a water contact angle greater than 150° with only 2-3% of the water drop to come into contact with its leaf, and is therefore considered a superhydrophobic surface. This property is attributed to the synergistic effect of two important factors such as (1) hierarchical roughness, which are the nanometer scale asperities within the micron scale geometrical structures and (2) low surface energy wax epicuticula on the surface of the leaf. Its high water resistance property is well worth mimicking because of the many industrial and practical applications namely self-cleaning, anti-fouling marine coatings, stain-resistant fabrics, oxidation resistant surfaces, anti-adhesive coatings, nano-battery, microfluidics, anti-biofouling, etc.
With the basic understanding of the natural design of a lotus leaf, an artificial superhydrophobic surface can be accomplished by developing a dual-scale roughness structure and tuning the surface energy of the surface. Recently, electrically conducting polymers with fluorinated functional group has been used extensively to make a surface that would confer water and also oil resistance. Conducting polymers have been also used to develop various types of industrial coatings for anti-corrosion and anti-static purposes. Furthermore, conducting polymers have unique electro-optical properties making them useful for display materials, semi-conductors, electrochromic devices, fluorescent materials, non-linear optical materials, electromagnetic shielding, etc.
Unlike the other methods of creating polymer coatings such as electrospinning, lithography, and layer-by-layer assembly, the electrochemical deposition offers the following advantages like inexpensive, fast and easy to use. It has been used on a variety of electrode surfaces mostly based on metal or semi-conductor and transparent substrates such as Au, Ag, Al, stainless steel, indium tin oxide (ITO), etc. This includes similarly, the vertical deposition method also called the Langmuir-Blodgett (LB) like-technique used for the layering of polystyrene particles on conducting surface, which does not necessarily require a sophisticated technology.
Thus, there is a need in the art for new efficient and cost effective techniques for making a highly-ordered and closely packed arrays of the latex microspheres on flat surfaces having unique electrochromic and wettability properties.